This invention relates generally to apparatus for measuring weight per unit length (e.g., denier) of yarn, and more particularly to an improved, automatic apparatus for prestripping a specified length of yarn from a package, metering a measured length of yarn under constant tension into a scale pan, weighing this specimen to determine the denier therefrom, and finally removing the weighed yarn sample.
In the past, when absolute denier values were required, measurements were usually made by winding a specimen skein of yarn on a reel, manually transferring this specimen to a weighing device, and then computing denier from specimen weight and length. More recently, yarn specimens are prepared by automatically drawing yarn from a package by means of a pair of metering rolls and projecting a measured length of this yarn either into a coiling device or directly onto a pan of a weighing device. One of the problems encountered in deniering yarn is the inaccuracy of measurements experienced when the outside layer of the yarn on the yarn package is used for such measurements. This problem occurs because the yarn on the outside of a yarn package may not only be more likely damaged, but it also may show the effects of tension variations during doffing. Since these in turn affect determination of denier, it is desirable to strip this outer layer from the package and use yarn from a nonexposed portion of the package to assure more accurate denier measurements. To accomplish this requires that yarn be prestripped from the package by some means. Furthermore, when multiple measurements are being made from one package, prior art devices require that the yarn draw-off be stopped when each yarn specimen is cut off, and that the standing part of the yarn which comes from the yarn package source be restrained while the cut yarn specimen is transferred to the weighing pan and/or weighed, even so, yarn length measurement errors arise out of pretension variations resulting from stopping and starting yarn draw-off in the course of a measurement series. This effect is particularly noticeable when measuring high bulk or textured yarns such as BCF, or other easily stretched yarns. Prior art prestripping and measurement techniques are time consuming as well.
The present invention provides a device for continuous draw-off of yarn from a package at a measured rate and under regulated tension. This yarn either is passed to waste for a predetermined length of time or is metered to the pan of a weighing device for subsequent determination of yarn weight per unit length. Diversion of the running yarn from one path to the other is achieved without affecting yarn draw-off rates and tensions.